Add support for COPY from previous rootfs

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

integration-cli/docker_cli_build_test.go

@@ -5755,6 +5755,138 @@ func (s *DockerSuite) TestBuildContChar(c *check.C) {
 	c.Assert(result.Combined(), checker.Contains, "Step 2/2 : RUN echo hi \\\\\n")
 }
 
+func (s *DockerSuite) TestBuildCopyFromPreviousRootFS(c *check.C) {
+	dockerfile := `
+		FROM busybox
+		COPY foo bar
+		FROM busybox
+    %s
+    COPY baz baz
+    RUN echo mno > baz/cc
+		FROM busybox
+    COPY bar /
+    COPY --from=1 baz sub/
+    COPY --from=0 bar baz
+    COPY --from=0 bar bay`
+	ctx := fakeContext(c, fmt.Sprintf(dockerfile, ""), map[string]string{
+		"Dockerfile": dockerfile,
+		"foo":        "abc",
+		"bar":        "def",
+		"baz/aa":     "ghi",
+		"baz/bb":     "jkl",
+	})
+	defer ctx.Close()
+
+	result := buildImage("build1", withExternalBuildContext(ctx))
+	result.Assert(c, icmd.Success)
+
+	out, _ := dockerCmd(c, "run", "build1", "cat", "bar")
+	c.Assert(strings.TrimSpace(out), check.Equals, "def")
+	out, _ = dockerCmd(c, "run", "build1", "cat", "sub/aa")
+	c.Assert(strings.TrimSpace(out), check.Equals, "ghi")
+	out, _ = dockerCmd(c, "run", "build1", "cat", "sub/cc")
+	c.Assert(strings.TrimSpace(out), check.Equals, "mno")
+	out, _ = dockerCmd(c, "run", "build1", "cat", "baz")
+	c.Assert(strings.TrimSpace(out), check.Equals, "abc")
+	out, _ = dockerCmd(c, "run", "build1", "cat", "bay")
+	c.Assert(strings.TrimSpace(out), check.Equals, "abc")
+
+	result = buildImage("build2", withExternalBuildContext(ctx))
+	result.Assert(c, icmd.Success)
+
+	// all commands should be cached
+	c.Assert(strings.Count(result.Combined(), "Using cache"), checker.Equals, 7)
+
+	err := ioutil.WriteFile(filepath.Join(ctx.Dir, "Dockerfile"), []byte(fmt.Sprintf(dockerfile, "COPY baz/aa foo")), 0644)
+	c.Assert(err, checker.IsNil)
+
+	// changing file in parent block should not affect last block
+	result = buildImage("build3", withExternalBuildContext(ctx))
+	result.Assert(c, icmd.Success)
+
+	c.Assert(strings.Count(result.Combined(), "Using cache"), checker.Equals, 5)
+
+	c.Assert(getIDByName(c, "build1"), checker.Equals, getIDByName(c, "build2"))
+
+	err = ioutil.WriteFile(filepath.Join(ctx.Dir, "foo"), []byte("pqr"), 0644)
+	c.Assert(err, checker.IsNil)
+
+	// changing file in parent block should affect both first and last block
+	result = buildImage("build4", withExternalBuildContext(ctx))
+	result.Assert(c, icmd.Success)
+	c.Assert(strings.Count(result.Combined(), "Using cache"), checker.Equals, 5)
+
+	out, _ = dockerCmd(c, "run", "build4", "cat", "bay")
+	c.Assert(strings.TrimSpace(out), check.Equals, "pqr")
+	out, _ = dockerCmd(c, "run", "build4", "cat", "baz")
+	c.Assert(strings.TrimSpace(out), check.Equals, "pqr")
+}
+
+func (s *DockerSuite) TestBuildCopyFromPreviousRootFSErrors(c *check.C) {
+	dockerfile := `
+		FROM busybox
+		COPY --from=foo foo bar`
+
+	ctx := fakeContext(c, dockerfile, map[string]string{
+		"Dockerfile": dockerfile,
+		"foo":        "abc",
+	})
+	defer ctx.Close()
+
+	buildImage("build1", withExternalBuildContext(ctx)).Assert(c, icmd.Expected{
+		ExitCode: 1,
+		Err:      "from expects an integer value corresponding to the context number",
+	})
+
+	dockerfile = `
+		FROM busybox
+		COPY --from=0 foo bar`
+
+	ctx = fakeContext(c, dockerfile, map[string]string{
+		"Dockerfile": dockerfile,
+		"foo":        "abc",
+	})
+	defer ctx.Close()
+
+	buildImage("build1", withExternalBuildContext(ctx)).Assert(c, icmd.Expected{
+		ExitCode: 1,
+		Err:      "invalid from flag value 0 refers current build block",
+	})
+}
+
+func (s *DockerSuite) TestBuildCopyFromPreviousFrom(c *check.C) {
+	dockerfile := `
+		FROM busybox
+		COPY foo bar`
+	ctx := fakeContext(c, dockerfile, map[string]string{
+		"Dockerfile": dockerfile,
+		"foo":        "abc",
+	})
+	defer ctx.Close()
+
+	result := buildImage("build1", withExternalBuildContext(ctx))
+	result.Assert(c, icmd.Success)
+
+	dockerfile = `
+		FROM build1:latest
+    FROM busybox
+		COPY --from=0 bar /
+		COPY foo /`
+	ctx = fakeContext(c, dockerfile, map[string]string{
+		"Dockerfile": dockerfile,
+		"foo":        "def",
+	})
+	defer ctx.Close()
+
+	result = buildImage("build2", withExternalBuildContext(ctx))
+	result.Assert(c, icmd.Success)
+
+	out, _ := dockerCmd(c, "run", "build2", "cat", "bar")
+	c.Assert(strings.TrimSpace(out), check.Equals, "abc")
+	out, _ = dockerCmd(c, "run", "build2", "cat", "foo")
+	c.Assert(strings.TrimSpace(out), check.Equals, "def")
+}
+
 // TestBuildOpaqueDirectory tests that a build succeeds which
 // creates opaque directories.
 // See https://github.com/docker/docker/issues/25244